Saturn

Saturn, the sixth planet from the Sun, is named for the Roman god of
agriculture, who was based on the Greek god Cronus. The second largest
planet in the solar system, it measures almost 75,000 miles (120,600
kilometers) in diameter at its equator. Despite its large size, Saturn is
the least dense of all the planets. It is almost 30 percent less dense
than water; placed in a large-enough body of water, Saturn would float.

Saturn completes one rotation on its axis very quickly, roughly 10.5 Earth
hours. As a result of this spinning, the planet has been flattened at its
poles. The measurement around its equator is 10 percent greater than the
measurement around the planet from pole to pole. In contrast to the length
of its day, Saturn has a very long year. Lying an average distance of 887
million miles (1.4 billion kilometers) from the Sun, Saturn takes 29.5
Earth years to complete one revolution.

Saturn consists primarily of gas. Its hazy yellow clouds are made of
crystallized ammonia, swept into bands by fierce, easterly winds that have
been clocked at up to a speed of 1,100 miles (1,770 kilometers) per hour
at its equator. Winds near the poles, however, are much tamer. Covering
Saturn's surface is a sea of liquid hydrogen and helium that
gradually becomes a metallic form of hydrogen. This sea conducts strong
electric currents that, in turn, generate the planet's powerful
magnetic field. Saturn's core, which is several times the size of
Earth, is made of rock and ice. The planet's atmosphere is composed
of about 97 percent hydrogen, 3 percent helium, and trace amounts of
methane and ammonia. Scientists estimate the surface temperature to be
about −270°F (−168°C).

About every 30 years, following Saturn's summer, a massive storm
takes place on the planet. Known as the Great White Spot, it is visible
for nearly a month, shining like a spotlight on the planet's face.
The spot then begins to break up and stretch around the planet as a thick
white strip. The storm is thought to be a result of the warming of the

Saturn, the second largest planet in the solar system, and its system
of rings.
(Reproduced by permission of

National Aeronautics and Space Administration

.)

atmosphere, which causes ammonia to bubble up, solidify, and then be
whipped around by the planet's monstrous winds.

Saturn's rings

Saturn's most outstanding characteristic are its rings. The three
other largest planets (Jupiter, Uranus, and Neptune) also have rings, but
Saturn's are by far the most spectacular. For centuries,
astronomers thought the rings were moons. In 1658, Dutch astronomer
Christiaan Huygens first identified the structures around Saturn as a
single ring. In later years, equipped with stronger and stronger
telescopes, astronomers increased the number of rings they believed
surrounded the planet.

In 1980 and 1981, the
Voyager 1
and
Voyager 2
space probes sent back the first detailed photos of Saturn and its
spectacular rings. The probes revealed a system of over 1,000 ringlets
encircling the planet at a distance of 50,000 miles (80,450 kilometers)
from its surface.

Saturn's rings, as seen by
Voyager
in November 1980.
(Reproduced by permission of

National Aeronautics and Space Administration

.)

The rings, which are estimated to be one mile (1.6 kilometers) thick, are
divided into three main parts: the bright A and B rings and the dimmer C
ring. The A and B rings are divided by a gap called the Cassini Division,
named for it discoverer, seventeenth-century French astronomer Giovanni
Domenico Cassini. The A ring itself contains a gap, called the Encke
Division after German astronomer Johann Encke, who discovered it in 1837.
The Encke Division contains no matter, but the Voyager missions found that
the Cassini Division contains at least 100 tiny ringlets, each composed of
countless particles. Voyager confirmed the existence of puzzling radial
lines in the rings called "spokes," which were first
reported by amateur astronomers. Their nature remains a mystery, but may
have something to do with Saturn's magnetic field. Saturn's
outermost ring, the F ring, is a complex structure made up of several
smaller rings along which "knots" are visible. Scientists
speculate that the knots may be clumps of ring material, or mini moons.

While scientists do not know the full composition of the rings, they do
know that the rings contain dust and a large quantity of water. The water
is frozen in various forms, such as snowflakes, snowballs, hailstones, and
icebergs. The forms range in size from about 3 inches (7.6 centimeters) to
30 feet (9 meters) in diameter. Scientists are also not sure how the rings
were formed. One theory states that they were once larger moons that were
smashed to tiny pieces by comets or meteorites. Another theory holds that
the rings are pre-moon matter, cosmic fragments that never quite formed a
moon.

Saturn's moons

Saturn has 18 known moons that have received officially sanctioned names
from the International Astronomical Union. In late 2000, astronomers
detected up to twelve possible new moons orbiting the planet, some at a
distance between 6.2 and 12.4 million miles (10 and 20 million
kilometers). These have all been given provisional designations, but
scientists believe only six out of the twelve may turn out to be real
moons. All the known moons are composed of about 30 to 40 percent rock and
60 to 70 percent ice. All but two have nearly circular orbits and travel
around Saturn in the same plane.

Christiaan Huygens discovered Saturn's first moon Titan, in 1655.
It is the only moon in the solar system with a substantial atmosphere,
which is composed mainly of nitrogen.
Voyager 1
revealed that Titan may have seas of liquid methane bordered by organic
tarlike matter. Titan's thick blanket of orange clouds, however,
prevent a direct view of the surface.

Cassini mission to Saturn

The
Cassini
orbiter, which was launched in October 1997, will deliver much more
information about Saturn and its moons. With a budget of $3.4 billion, it
is the last of the National Aeronautics and Space Administration's
(NASA) big-budget, big-mission planetary probes.
Cassini,
which weighs nearly 13,000 pounds (5,900 kilograms), carries 18
scientific instruments that will take a variety of measurements of
Saturn's atmosphere, its moons, and the dust, rock, and ice that
comprise its rings. After traveling some 2.2 billion miles (1 billion
kilometers), the orbiter is scheduled to arrive at Saturn in mid-2004. It
carries with it a probe, called
Huygens,
that was built by the European Space Agency. The probe will drop onto the
surface of Titan for a detailed look at the moon's surface. If it
survives the impact of its landing,
Huygens
will transmit data from the surface back to
Cassini
for up to 30 minutes. After releasing the probe,
Cassini
will orbit Saturn at least 30 times over a four-year period, gathering
information and sending back more than 300,000 color images taken with an
onboard camera.

User Contributions:

One theory was that scientists thought rings were once larger than moons and then hit by space objects and broken up. Why didn't the pieces of the moon just fly off into space, instead of collecting in rings around the planet? Is it because of the magnetic field it has.